The present invention relates to an apparatus for the production of colloidal mixtures, especially castable respectively sprayable colloidal water-cement mixtures, which may contain additional solid additions. The present invention relates also to a method for producing such colloidal mixtures.
The production of colloidal water-cement mixtures for producing of the colloidal concrete requires specific mixing apparatus. Such mixtures are produced in that energy is introduced into the extensively mixed components. Due to the introduced energy the individual cement particles are extensively wetted and it is possible to transform the mixture into colloidal condition, that is into a condition in which neither liquid water nor solid cement particles are present but an extensively blended homogeneous mixture, which exists in a single phase.
The introduction of energy into an initially present two-phase system, consisting of water and therein suspended solid cement, is of course best carried out by a suitable stirrer.
The DE-OS No. 27 18 236 describes a method in which cement and water at a ratio of 0.25:0.6 is premixed in a mixer during a time period of about 2 minutes with a circumferential speed of the mixture of about 300 meters per minute and subsequently thereto subjected for at least 8 minutes to a mass acceleration of at least 2 g (g=9.81 meters/sec.sup.2).
A further method is described in the Luxembourg Pat. No. 81,524, assigned to the same assignee, in which water in the amount of 25-60% of the final mixture is rotated in a container by means of a stirrer having at its outer diameter a circumferential speed of at least 1,500 meters per minute, in which cement is then introduced into the mixture while maintaining the rotational speed of the stirrer or by reducing the speed to at most the half of the mentioned circumferential speed, and wherein subsequently thereto sand in the amount of 2 parts for each cement part with a moisture content of 5-15% is introduced into the mixture in such a manner that the sand is fed into the center of the funnel-shaped profile formed in the mixture by the stirring.
It has been ascertained that the addition of sand causes, surprisingly, that cements of lesser quality, even though they can be well colloided but which produced quite often mixtures without sufficient adhesion characteristics, may be used in accordance with this method, which evidently results in considerable advantages as to production costs and supply of raw material.
Such colloidal water cement mixtures with or without further solids addition serves especially for the coating of cast steel parts, such as conduits, boilers, containers, and the like. Such mixtures are especially used to replace expensive corrosion-preventing films, lacquers or plastic coating in a cost-saving manner. A main advantage of such colloidal mixtures consists in that the steel parts which have to be coated do not require a surface treatment, for instance by sand blasting, which increases the cost of conventional corrosion protection to a considerable degree.
It has, however, been ascertained that even small deviations from the individual method charateristics above described, as for instance a too high or too low moisture content of the sand or a inexact introduction of the sand, lead to a failure of the above described production process.
Thus, if the sand is not correctly introduced into the mixture in the manner as described above, the mixture may rise along the inner surface of the mixture and settle there, while a cavity forms around the blades of the mixer in which the blades rotate without producing any action.
Furthermore, the mixing time should not be surpassed in order to avoid a premature settling of the mixture, while at the same time it is necessary to carry out the mixing and stirring as long and as intensively as possible since this is a necessary precondition for proper colloiding.